Iran began a worldwide search for large quantities of grain to make up for supplies of grain from the United States. The last American grain shipment to Iran was a 32,000 ton cargo that left Portland, Oregon on Nov, 6, 1979.US wheat farmers considered a boycott not to be in their best interest.On Nov, 6, 1979, after the U.S. permitted the exiled Shah of Iran to enter the United States for medical treatment, and after rumors of another U.S. backed coup and re-installation of the Shah (as it had happened during Operation TP-AJAX in 1953), a group of radical students took action in Tehran by seizing the American Embassy and taking hostage the people inside calling it the Spy Den. The United States responded by freezing about 12 billion USD in Iranian assets, including bank deposits, gold and other properties. Some assets - Iranian officials say 10 billion USD, U.S. officials say much less - still remain frozen pending resolution of legal claims arising from the revolution.After the invasion of Iran by Iraq on Sep, 22, 1980 which was reportedly initiated by a nod from Americans, US increased sanctions against Iran. In 1984, sanctions were approved that prohibit weapons sales and all U.S. assistance to Iran. The United States also opposed all loans to Iran from international financial institutions. In 1987, the United States further prohibited the importation and exportation of any goods or services from Iran.The effects of US sanctions on Iran have mostly damaged the two countries in that Iranian consumers have been forced to look for other suppliers worldwide. This has affected US suppliers and their worldwide reputation indeed while opening the door to third parties and middlemen on both sides who take the lion share. In 2011, U.S. sanctioned, two Israeli-owned firms for violating Iran sanctions depicting a somehow shocking but visible fact that Israel wants to make money, as in selling weapons to Iran during its war with Iraq, Israel knows how to close its eyes on its enemy;)